Neutral Size for SFD

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wrobotronic

wrobotronic

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Colorado
Would someone be so kind as to point me to where the NEC 2014 will indicate that the Neutral can be smaller than the ungrounded conductors for a 200A service to a SFD...

Basically, If I run 4/0 AL for my service what size can I make the neutral?

Thank you very much everyone....
 
augie47 said:
Don't overlook 250.24(C) in regard to "minimum size"
Click to expand...

Just so I am clear on this: My conductors are 4/0 Al for a 200A SFD service. Then by Table 250.102C1 My neutral (grounded conductor) only has to be #2Al?

My gut tells me im wrong on this. I have never sized a service per se, I have always just done what the drawings/ foreman have said. Normally, I use 4/0Al for 3 conductors and a #2Al for my grounding electrode conductor.

I am making this harder than it needs to be... which honestly needs to be my signature because I seem to post that statement quit a bit... :)

Thank you all for your help....
 
Think of the neutral as a white wire with an imaginary green stripe. It carries unbalanced current (white) or serves as a ground fault return (green). You can calculate the unbalanced current or do what everyone else does, just use 2/0. Why 2/0? Thats the way it comes with 4/0 4/0 2/0. Many code cycles ago the neutral was two trade sizes smaller than the ungrounded, so that practice still carries over, I need to look to see when this was changed, or maybe someone else will know
if you use 2 AL the inspector will not of seen that before, will want to see the calcs, and may look closer at your install.
I like to have my students understand the code and what the reasoning is.
 
wrobotronic said:
Just so I am clear on this: My conductors are 4/0 Al for a 200A SFD service. Then by Table 250.102C1 My neutral (grounded conductor) only has to be #2Al?

My gut tells me im wrong on this. I have never sized a service per se, I have always just done what the drawings/ foreman have said. Normally, I use 4/0Al for 3 conductors and a #2Al for my grounding electrode conductor.

I am making this harder than it needs to be... which honestly needs to be my signature because I seem to post that statement quit a bit... :)

Thank you all for your help....
Click to expand...

You are correct in that a #2 AL is the smallest size you could run based on Art 250, however, 220.61 calculations may require a larger wire. You can perform the calculations (Mike Holt;'s home page has a nice calculation form in "Free Stuff") or, as Tom mentioned above, you could
use a 2/0AL and most inspectors would not question the reduction as it would be almost impossible for a 200 amp service to require larger.
 
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